Method for producing high-strength hot-dip galvannealed steel sheet

ABSTRACT

Exemplary embodiments of the present invention can provide a method for producing hot dip galvannealed steel sheet which exhibits high strength, high ductility, and a significant degree of alloying. Such exemplary method can be applied to, e.g., a pickled hot rolled steel sheet or an annealed and pickled cold rolled steel sheet containing between about 0.02% and about 0.2% C and between about 0.15% and about 2.5% Mn, and may include one or more procedures for rinsing the sheet, preplating the sheet with Ni, rapidly heating the sheet in a nonoxidizing atmosphere to a sheet temperature of about 430° C. to 500° C., then hot dip plating the sheet in a galvanizing bath containing between about 0.05% and about 0.2% Al, and then immediately heating the sheet rapidly for an alloying treatment. Such exemplary method can provide an improved alloying speed, improved plating appearance and better plating adhesion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of PCT Application No.PCT/JP2006/308376 which was filed on Apr. 14, 2006, and published onOct. 26, 2006 as International Publication No. WO 2006/112520. Thisapplication claims priority from the International Application pursuantto 35 U.S.C. § 365, and from Japanese Patent Application No.2005-121830, filed Apr. 20, 2005, and Japanese Patent Application No.2005-145023, filed May 18, 2005, under 35 U.S.C. § 119. The entiredisclosures of the above-referenced applications are incorporated hereinby reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a method for producing high-strengthhot-dip galvannealed steel sheet, including, e.g., including autilization of Ni preplating to obtain a good plating performance and toreduce or minimize a deterioration in quality which may arise from aheat treatment during hot-dip galvanization and/or an alloyingtreatment.

BACKGROUND INFORMATION

High strength, high ductility steel sheets can be used for internal andexterior body panels, chassis parts, etc., for reducing the weight ofautomobiles. Hot-dip galvannealed steel sheet may be used in suchapplications to provide good corrosion resistance. However, C and Mnwhich may be added to steel (e.g., steel sheet) to increase strength canretard alloying during galvanization. Obtaining both strength and asufficient degree of alloying in such steel sheet can be difficult. Forexample, a steel sheet containing about 0.2% or more Si can exhibitinsufficient wettability of the plating, and alloying may also notproceed easily, when applying a conventional Senzimir typehot-SUBSTITUTE dip galvanizing technique to such steel sheet.

A method for producing hot-dip galvannealed steel sheet which utilizesNi preplating of a base steel sheet containing 0.2% to 0.5% Si, whichmay help to address these shortcomings, is described, e.g., in JapanesePatent No. 2526320, the entire disclosure of which is incorporatedherein by reference.

For example, a presence of P in steel can inhibit and delay an alloyingreaction of zinc. An alloying time longer than that used for ordinarysteel sheet may be required, which can reduce productivity. Further,when using a single manufacturing line to produce both steel sheet witha fast alloying speed (for example, ultralow carbon steel sheet to whichTi or Nb is added) and steel sheet to which P is added, it may benecessary to optimally manage an Al concentration in the hot-dipgalvanizing bath, alloying treatment conditions, etc., and thusprocessing of such materials may become complicated.

In view of the problems described herein, it may be desirable to improvealloying speed of P-containing steel sheet. For example, a processingtechnique which includes preplating high tension steel sheet containingP with Ni, heating it under predetermined conditions, hot-dipgalvanizing it, then heat alloying it under predetermined conditions isdescribed, e.g., in Japanese Patent No. 2526320, the entire disclosureof which is incorporated herein by reference. However, it may still bedifficult to produce high strength, high ductility hot-dip galvannealedsteel sheet exhibiting a strength greater than 590 MPa using thetechnique described in this Japanese patent. A long soaking time mayalso be preferred to secure a sufficient degree of alloying when usingsuch technique. As a result, both strength and ductility can dropsignificantly, so application of this technique to automobile internaland exterior body panels, chassis parts, etc. having a complicated shapemay be limited. Further, when applying the technique described in thisJapanese patent to a base steel sheet containing P, a plating appearancemay likely become uneven, which may thus be unsuitable for automobileapplications, e.g., for sheet used as exterior panels.

A further processing technique which includes annealing P-containingsteel sheet, pickling such steel sheet, cleaning the surface, thengalvanizing it, plating it, and heat alloying it is described, e.g., inJapanese Patent Publication (B2) No. 7-9055, the entire disclosure ofwhich is incorporated herein by reference. A heat alloying treatmenttime used in this technique can be relatively long, and obtaining anappearance of sufficient quality for application to automobiles, inparticular for external panels, may be difficult.

SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION

To address at least some of the problems described herein, exemplaryembodiments of the present invention can provide a method for producinghot-dip galvannealed steel sheet which can achieve high strength, highductility, and a significant degree of alloying. Further, exemplaryembodiments of the present invention can provide a method for hot-dipgalvannealing P-containing steel sheet which allows both an improvementin alloying speed and improved performance of the galvannealing process,such as a good plating appearance and an improved plating adhesion.

For example, a reduction in the strength and ductility can be reduced orminimized by using alloying heat treatment conditions in a hot-dipgalvannealing process which include rapidly heating the steel sheet to atemperature between about 470° C. and 550° C. at a heating rate of about30° C./sec or more, holding at the high temperature to soak for lessthan about 10 seconds, and then cooling the sheet. However, suchalloying conditions may not achieve a desired degree of alloying. Forexample, alloying under such conditions may proceed poorly when using asteel sheet containing Si. However, a state of the base sheet used andpretreatment conditions for a Ni preplating may be optimized inaccordance with exemplary embodiments of the present invention toachieve high strength, high ductility, and a sufficient degree ofalloying.

Thus, exemplary embodiments of the present invention can provide amethod which includes, e.g., pickling (i) a pickled hot rolled steelsheet containing between about 0.02% and about 0.2% C, and between about0.15% and about 2.5% Mn as primary components, or (ii) an annealed andpickled cold rolled steel sheet, rinsing the sheet and, without dryingthe sheet, preplating it with an amount of Ni between about 0.2 andabout 2.0 g/m². The sheet may be rapidly heated in a nonoxidizing orreducing atmosphere to a sheet temperature of about 430° C. to 500° C.at a heating rate of about 30° C./sec or more. The sheet may then behot-dip plated in a galvanizing bath containing between about 0.05% andabout 0.2% Al, wiped, then immediately heated to a temperature of about470° C. to 550° C. at a heating rate of about 30° C./sec or more.Further, the sheet can be cooled without taking any soaking time, orholding it to soak for less than about 10 seconds and then cooling it.The rinsing water used after the pickling treatment may preferably havea pH of less than about 6. In certain exemplary embodiments of thepresent invention, Ni can be preplated after the pickling treatmentwithout rinsing or drying. The steel sheet used may also contain betweenabout 0.2% and about 3% Si.

The processing of a high steel sheet containing 0.02% or more of P isdescribed, e.g., in Japanese Patent Publication (B2) No. 7-9055.Exemplary embodiments of the present invention can provide an improvedalloying speed and a good plating appearance as compared to thetechnique described in this Japanese publication, even when an Alconcentration in the hot-dip galvanizing bath is high. PicklingP-containing steel sheet after annealing two times can be effective forachieving such results. For example, certain exemplary embodiments ofthe present invention can provide a method for producing high-strengthhot-dip galvannealed steel sheet which includes, e.g., pickling annealedhigh-strength steel sheet containing about 0.02% or more of P, dryingthe sheet and further pickling it, then preplating the sheet with Ni,heating it in a nonoxidizing atmosphere to a temperature of about 430°C. to 500° C., plating the sheet in a hot-dip galvanizing bathcontaining between about 0.05% and about 0.2% Al, and then heat alloyingthe sheet.

Thus, exemplary embodiments of the present invention can provide amethod for producing hot-dip galvannealed steel sheet able to achieveboth high strength/high ductility and the alloying degree. Further,P-containing steel sheet can be hot-dip galvannealed with a highproductivity, and a good plating appearance and plating adhesion canalso be achieved.

These and other objects, features and advantages of the presentinvention will become apparent upon reading the following detaileddescription of embodiments of the invention, when taken in conjunctionwith the appended claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Exemplary embodiments of the present invention may be used to processsteel sheet containing between about 0.02% and about 0.2% C, and betweenabout 0.15% and about 2.5% Mn. In addition, between about 0.2% and about3% Si may also be present.

A state of the base sheet used can be important for processing inaccordance with exemplary embodiments of the present invention. Forexample, a pickled hot rolled steel sheet or an annealed and pickledcold rolled steel sheet can be used. Various conventional picklingtechniques may be used for the hot rolled steel sheet to remove anysurface scale which may be present. Applying a cooling procedure usingwater (such as, e.g., vaporization cooling) to a steel sheet may likelyform with a scale on the surface, so a conventional technique forpickling such cold rolled steel sheet at a back surface in the annealingline can be performed. Such sheet can be used as a base sheet inexemplary embodiments of the present invention. However, sheet passingthrough gas cooling, etc., during a cooling step may likely not bepickled at a back surface in the annealing line, and such steel sheetshould be pickled for use in accordance with exemplary embodiments ofthe present invention.

When the pickled hot rolled steel sheet or annealed, pickled cold rolledsteel sheet described above are preplated with Ni, pickling can beperformed as a pretreatment. For example, pickling twice when combinedwith the pickling of the base sheet can be performed in accordance withexemplary embodiments of the present invention. Thus, a significantdegree of alloying can be achieved under conditions which may avoiddeterioration of strength and/or ductility of the sheet.

A number of pickling treatments can be determined in accordance withexemplary embodiments of the present invention. For example, a steelsheet may pass through a plurality of pickling tanks. However, if thesteel sheet is not dried between one tank and another tank, even if aplurality of tanks are used, the pickling procedure can be considered tobe a single treatment. By drying the sheet (e.g., rinsing and thendrying) after crystal grains are corroded due to the pickling, oxygen inthe atmosphere may cause a surface of the sheet to be thinly oxidized.Repeated pickling of the surface of the steel sheet in such oxidizedstate can allow C and Mn to be removed uniformly and effectively, and,as a result, a high alloying speed and uniform plating appearance can beachieved. Thus, drying of the steel sheet between one pickling treatmentand another pickling treatment can be important.

Pickling may be performed using, e.g., an aqueous solution of sulfuricacid or hydrochloric acid. Other acids may inhibit alloying, and thusmay not be preferred. The sheet may be degreased to remove any dirtbefore a main pickling treatment, and mechanical grinding, e.g., usingbrushes, etc., may also be performed.

Conditions used for rinsing which may be performed after a picklingtreatment can also be important. For example, rinsing followed by dryingmay preferably be avoided before the Ni preplating procedure. Further, apH of the rinsing water may preferably be less than about 6. Ni may alsobe preplated onto the sheet as-is after pickling, e.g., withoutsubsequent rinsing or drying. If the above conditions are not met,alloying may be inhibited.

In exemplary embodiments of the present invention, the amount of Nipreplating can be between about 0.2 g/m² and about 2 g/m². If the amountof Ni is less than the lower limit, the wettability of the plating maybecome insufficient or a sufficient degree of alloying may not beobtained. Preplating Ni in an amount greater than the upper limit maynot provide further beneficial effects (e.g., the effect of Ni becomessaturated), and the use of such excess Ni can be uneconomical. A varietyof Ni preplating conditions may be used such as, e.g., a sulfuric acidbath, a chlorination bath, a watt bath, a sulfamic acid bath, or otherconventional baths.

After preplating with Ni, the sheet can be rapidly heated in anonoxidizing or reducing atmosphere to a sheet temperature of about 430°to 500° C. at a heating rate of about 30° C./sec or more. This heattreatment can secure wettability of the hot-dip plating and improveplating adhesion. After this heating procedure, the sheet can be hot-dipgalvanized and wiped to adjust the basis weight. The concentration of Alin the hot-dip galvanizing bath can be between about 0.05% and about0.2%. If less than about 0.05% Al is present in the bath, the platingadhesion may easily deteriorate, while if over 0.2% Al is present,achieving both sufficient alloying and quality can become difficult.

After the sheet is wiped, it can be heated to a temperature of about470° C. to 550° C. at a heating rate of about 30° C./sec or more. Thesheet can then be cooled without any soaking time, or it can be held forsoaking for less than about 10 seconds and then cooled, to alloy thesheet. This procedure can be important for preventing or minimizing adeterioration of strength and ductility, and for achieving a sufficientdegree of alloying.

Hot-dip galvannealing of P-containing steel sheet can also be achievedin accordance with certain exemplary embodiments of the presentinvention. For example, a P-containing steel sheet such as, e.g., a hotrolled sheet, a cold rolled sheet, a low carbon steel sheet, an ultralowcarbon steel sheet, etc. may be used. Further, steel sheet containingso-called “trump elements” such as Cr, Cu, Ni, and Sn may also be used.Exemplary embodiments of the present invention can achieve both a highalloying speed and a good plating appearance, so they may beparticularly effective for processing cold rolled ultralow carbon steelsheet for which a good plating appearance may be desirable. If about0.02% or more of P is present, alloying may be significantly retardedand there may be a significant drop in productivity of the process.Thus, exemplary embodiments of the present invention may be particularlyeffective for steel sheet containing about 0.02% or more of P.

Certain exemplary embodiments of the present invention can includeseveral pickling procedures of a P-containing steel sheet afterannealing. For example, certain actions and effects of a first picklingtreatment after annealing are described, e.g., in Japanese PatentPublication (B2) No. 7-9055. Annealing to form crystal grains, thenreducing the P present in concentrated amounts at crystal grains bypickling can contribute to an improvement of alloying speed. However,when using such a procedure to remove P the crystal grains can be deeplycorroded, which may result in a rough surface. Thus, a subsequentplating appearance can become irregular. Further, removal of P which maybe present at surfaces inside the crystal grains may not be sufficient,so the improvement in alloying speed can be small.

A variety of pickling procedures may be used in accordance withexemplary embodiments of the present invention. For example, picklingmay be performed using conditions such as those described, e.g., inJapanese Patent Publication (B2) No. 7-9055. Such conditions can includetreatment of a sheet with a 1% to 5% hydrochloric acid aqueous solutionat a temperature of about 60° C. to 90° C. for about 1 to 10 seconds. Asecond pickling treatment (or, when pickling more than two times, afinal pickling treatment) may also be significant for smoothing roughsurface conditions which may be formed by the first pickling (or, whenpickling more than two times, the immediately prior pickling treatment).Thus, a sulfuric acid treatment may be preferable to a hydrochloric acidtreatment for later or final pickling treatments. For example, atreatment in a 5% to 15% sulfuric acid aqueous solution at a temperaturebetween room temperature and about 70° C. for about 1 to 10 seconds maybe used.

After the pickling treatment described herein, and before hot-dipgalvanizing, the steel sheet can be preplated with Ni and heated to atemperature of about 430° C. to 500° C. After this preplating, which canprovide surface activation, the sheet can be plated in a hot-dipgalvanizing bath containing between about 0.05% and 0.2% Al. If lessthan about 0.05% Al is present, a high alloying speed can be obtainedbut the plating adhesion may deteriorate. If more than about 0.2% Al ispresent, a sufficient alloying speed may not be achieved.

Alloying conditions which may be used after plating can include, e.g.,heating the sheet to a temperature of about 470° C. to 600° C. at aheating rate of about 20° C./sec or more, then cooling the sheet with nosoaking time, or holding the sheet for soaking for less than about 15seconds and then cooling. Such treatment can provide a good platingappearance and good plating adhesion, and productivity may not beimpaired.

Example 1

Exemplary procedures for producing high strength, high ductility hot-dipgalvannealed steel sheet can be performed in accordance with exemplaryembodiments of the present invention. For example, Table 1 listscharacteristics of base sheets used for such exemplary procedures. Basesheet 1 and base sheet 2 are cold rolled, annealed, pickled steelsheets. Base sheet 3 is a pickled hot rolled steel sheet. Qualities ofmaterials measured after temper rolling the base sheets are provided inTable 3.

The base sheets were degreased using the exemplary conditions providedin Table 2. Pickling of certain sheets was performed using exemplaryconditions listed in Table 3. Ni preplating was performed byelectroplating using exemplary conditions listed in Table 4.

After Ni preplating, the sheets were heated in a 3% H₂+N₂ atmosphere ata heating rate of about 30° C./sec up to a temperature of about 450° C.They were then immediately dipped in a hot-dip galvanizing bath(containing about 0.15% Al), held at 450° C. for about 3 seconds, andwiped to adjust the basis weight to about 50 g/m². The sheets were thenalloyed right above the wiping using predetermined heating rates,temperatures, and soaking times. The sheets were cooled gradually at arate of about 2° C./sec for 8 seconds, then rapidly cooled at a rate ofabout 20° C./sec. After cooling, the sheets were temper rolled atreduction rates of about 0.5%.

Exemplary process conditions and evaluation observations for the samplesheets are shown in Table 5. An alloying degree was determined bydissolving a plating layer of a sample in hydrochloric acid, chemicalanalysis was used to determine composition, and the percentage of Fe inthe plating layer was calculated. Samples exhibiting about 9% or more ofFe were labeled “Good,” while those exhibiting less than 9% of Fe werelabeled “Poor.” Material quality was assessed by measuring a value forTS×El (Mpa·%) of each sample, where TS represents a tensile strength,and EL represents an elongation value to failure. Samples whichexhibited less than a 10% drop in the value of TS×El as compared withthe original value for the base sheet (shown in Table 1) were labeled as“Good,” and samples which showed a decrease greater than 10% werelabeled as “Poor.”

TABLE 1 Test Base Sheet Material characteristics after temper rollingIngredients (mass %) YP TS EL Type C Mn Si P S (Mpa) (Mpa) (%) Base Cold0.07 1.87 0.45 0.015 0.006 368 621 32 sheet 1 rolled Base Cold 0.09 1.731.3 0.009 0.002 446 821 23 sheet 2 rolled Base Hot 0.2 1.59 1.58 0.0090.001 567 806 27 sheet 3 rolled

TABLE 2 Alkali Degreasing Conditions NaOH 50 g/liter Solutiontemperature 65° C. Dipping 10 sec

TABLE 3 Pickling Conditions H₂SO₄ 100 g/liter Solution temperature 60°C. Dipping 10 sec

TABLE 4 Ni Preplating Conditions Ingredients Concentration NiSO₄•6H₂O300 g/liter H₃BO₃  40 g/liter Na₂SO₄ 100 g/liter pH 2.7

TABLE 5 Sample Production Conditions and Evaluation Results AlloyingDrying Ni Rate of Evaluation results Base Pickling before Ni preplatingtemperature rise Temperature Soaking time Alloying sheet treat. Rinsingpreplating (g/m²) (° C./s) (° C.) (sec) degree Quality Remarks 1 Table 1Yes No 0.2 50 490 0 Good Good Ex. 1 1 Table 1 Yes No 0.3 50 490 0 GoodGood Ex. 2 1 Table 1 Yes No 1 50 490 0 Good Good Ex. 3 1 Table 1 No No0.3 50 490 0 Good Good Ex. 4 1 Table 1 Yes No 0.3 50 470 8 Good Good Ex.5 1 Table 1 Yes No 0.3 50 550 0 Good Good Ex. 6 2 Table 1 Yes No 0.3 50520 0 Good Good Ex. 7 3 Table 1 Yes No 0.5 50 530 0 Good Good Ex. 8 1 NoNo Yes 0.3 50 490 0 Poor Good Comp. Ex. 1a 1 Table 1 Yes Yes 0.3 50 4900 Poor Good Comp. Ex. 2a 1 No No Yes 0.3 30 500 20 Good Poor Comp. Ex.3a

As indicated by the results listed in Table 5, exemplary sheetsprocessed in accordance with exemplary embodiments of the presentinvention exhibited an excellent degree of alloying and a high materialquality.

Example 2

Certain exemplary embodiments of the present invention can also be usedfor hot-dip galvannealing method of a P-containing steel sheet. In thefollowing examples, cold rolled, annealed steel sheets having thecompositions shown in Table 6 were used.

TABLE 6 Ingredients of Test Base Sheets Ingredients wt % C Mn Si P S TiNb Base sheet 1 0.002 0.381 0.003 0.059 0.006 0.001 0.003 Base sheet 20.002 0.68 0.024 0.023 0.013 0.005 0.007 Base sheet 3 0.004 0.39 0.120.095 0.011 0.013 0.016 (Examples 9 to 11 and Comparative Example 4a)

Table 7 shows the exemplary combinations of base sheets and treatmentconditions used. After a first pickling, the exemplary sheets wererinsed and dried. Except for Comparative Example 4a, the sheets werepickled a second time, rinsed, and then preplated with Ni to adeposition amount of about 0.3 g/m² using the electroplating conditionsshown in Table 4. The exemplary pickling conditions used are shown inTable 8. After this procedure, the sheets were heated in a 3%hydrogen+95% nitrogen atmosphere at a rate of about 40° C./sec to atemperature of about 460° C., and then immediately dipped in a hot-dipgalvanizing bath held at about 455° C. which contained Al. The exemplarysheets were then wiped to adjust the plating to a basis weight of about60 g/m². The concentrations of Al provided in the hot-dip galvanizingbaths are as shown in Table 7. After wiping, the sheets were heated at arate of about 50° C./sec to the predetermined temperatures shown inTable 7, soaked for predetermined times, gradually cooled at a rate ofabout 10° C./sec for 3 seconds, and then cooled at a rate of about 20°C./sec to room temperature.

Evaluation of the exemplary procedures described herein was conducted asfollows:

-   -   Plating appearance: Sheets which exhibited no visual unevenness        and appeared to be uniform in appearance were labeled as “Good,”        while those exhibiting unevenness or patterns in appearance and        which may not be suitable for use (e.g., for automobile external        panel applications) were labeled as “Poor.”    -   Alloying degree: The plating layer of a sample sheet was        dissolved in hydrochloric acid, and chemical analysis was used        to determine its composition and thereby calculate the        percentage of Fe present in the plating layer. Samples        exhibiting 9% or more of Fe in the plating layer were labeled as        “Good,” and those exhibiting less than 9% of Fe in the plating        layer were labeled as “Poor.”    -   Plating adhesion: Sheets were bent into a 60° V shape, and        plating peeling at the bent portion was then evaluated using a        tape peeling technique. Samples exhibiting a peeling distance of        less than 2 mm were labeled as “Good,” and samples exhibiting a        greater peeling distance were labeled as “Poor.”

TABLE 7 Sample Preparation Conditions and Results of Evaluation AlloyingPickling Hot-dip galva- treatment Base treatment nization Al SoakingPlating Alloying Plating sheet 1st 2nd concentration % Temp. timeappearance degree adhesion Remarks Base Pickling a Pickling c 0.15 520 0Good Good Good Ex. 9 sheet 1 Base Pickling a Pickling c 0.15 520 0 GoodGood Good Ex. 10 sheet 2 Base Pickling a Pickling c 0.15 520 0 Good GoodGood Ex. 11 sheet 3 Base Pickling b — 0.15 530 15 Poor Good Good Comp.sheet 1 Ex. 4a

TABLE 8 Pickling Treatment Conditions Solution Concentration TemperatureTime Pickling a Hydrochloric acid 5% 80° C. 2 sec Pickling bHydrochloric acid 5% 80° C. 2 sec × 2 times* Pickling c Sulfuric acid10%  30° C. 5 sec *Pickling b included two seconds of treatment in eachof two pickling tanks. No rinsing or drying was performed between thepickling tanks.

As indicated by the results listed in Table 7, exemplary sheetsprocessed in accordance with exemplary embodiments of the presentinvention (e.g., Examples 9-11) exhibited an excellent degree ofalloying, plating appearance, and plating adhesion. These exemplaryresults were obtained with a short alloying treatment, as describedherein.

INDUSTRIAL APPLICABILITY

Exemplary embodiments of the present invention can produce hot-dipgalvannealed steel sheet exhibiting excellent quality and degree ofalloying degree. Certain exemplary embodiments of the present inventioncan further be used to hot-dip galvanneal P-containing steel sheet witha high productivity and achieve both good plating appearance and goodplating adhesion. The industrial value of such processing methods issignificant.

1-8. (canceled)
 9. A method for producing a high-strength hot-dipgalvannealed steel sheet, the method comprising: pickling ahigh-strength steel sheet; drying the high-strength steel sheet; furtherpickling the high-strength steel sheet; preplating the high-strengthsteel sheet with between about 0.2 g/m² and about 2.0 g/m of Ni; heatingthe high-strength steel sheet in a nonoxidizing atmosphere to atemperature between about 430° C. and about 500° C.; plating thehigh-strength steel sheet in a hot-dip galvanizing bath containingbetween about 0.05% and about 0.2% of Al; and alloying the high-strengthsteel sheet using a heat treatment to produce the high-strength hot-dipgalvannealed steel sheet.
 10. The method of claim 9, wherein thehigh-strength steel sheet comprises between about 0.2% and about 3% ofSi.
 11. The method of claim 9, wherein the high-strength steel sheet isan annealed sheet comprising at least about 0.02% of P.
 12. The methodof claim 11, wherein the high-strength steel sheet is alloyed by heatingthe high-strength steel sheet to a temperature between about 470° C. andabout 600° C. at a rate of at least about 20° C./sec, and cooling thehigh-strength steel sheet.
 13. The method of claim 12, wherein thehigh-strength steel sheet is cooled by at least one of (i) cooling thehigh-strength steel sheet without soaking the high-strength steel sheet,or (ii) holding the high-strength steel sheet for soaking for less thanabout 15 seconds and then further cooling the steel sheet.
 14. Themethod of claim 11, wherein the high-strength steel sheet is pickledusing an aqueous solution of hydrochloric acid, and wherein thehigh-strength steel sheet is further pickled using an aqueous solutionof sulfuric acid.
 15. The method of claim 14, wherein the high-strengthsteel sheet is alloyed by heating the high-strength steel sheet to atemperature between about 470° C. and about 600° C. at a rate of atleast about 20° C./sec, and cooling the high-strength steel sheet. 16.The method of claim 15, wherein the high-strength steel sheet is cooledby at least one of (i) cooling the high-strength steel sheet withoutsoaking the high-strength steel sheet, or (ii) holding the high-strengthsteel sheet for soaking for less than about 15 seconds and then furthercooling the steel sheet.
 17. A method for producing a high-strengthhot-dip galvannealed steel sheet, the method comprising: pickling asteel sheet comprising at least one of (i) a pickled hot rolled steelsheet comprising between about 0.02% and about 0.2% of C, between about0.15% and about 2.5% of Mn, and a balance of Fe and unavoidableimpurities, or (ii) an annealed and pickled cold rolled steel sheet;rinsing the steel sheet; preplating the steel sheet with between about0.2 g/m² and about 2.0 g/m² of Ni without drying the steel sheet afterthe steel sheet is rinsed; preparing the steel sheet by heating thesteel sheet in at least one of a nonoxidizing atmosphere or a reducingatmosphere to a sheet temperature of about 430° C. to 500° C. at a rateof at least about 30° C./sec; hot-dip plating the steel sheet in agalvanizing bath comprising between about 0.05% and about 0.2% of Al;wiping the steel sheet; immediately heating the steel sheet to atemperature between about 470° C. and about 550° C. at a rate of atleast about 30° C./sec; and cooling the steel sheet to form thehigh-strength hot-dip galvannealed steel sheet.
 18. The method of claim17, wherein the steel sheet is cooled by at least one of (i) cooling thesteel sheet without soaking the steel sheet, or (ii) holding the steelsheet for soaking for less than about 10 seconds and then furthercooling the steel sheet.
 19. The method of claim 18, wherein the steelsheet comprises between about 0.2% and about 3% of Si.
 20. The method ofclaim 18, wherein the steel sheet is rinsed using a rinsing water havinga pH that is less than about
 6. 21. The method of claim 20, wherein thesteel sheet comprises between about 0.2% and about 3% of Si.
 22. Amethod for producing a high-strength hot-dip galvannealed steel sheet,the method comprising: pickling a steel sheet comprising at least one of(i) a pickled hot rolled steel sheet comprising between about 0.02% andabout 0.2% of C, between about 0.15% and about 2.5% of Mn, and a balanceof Fe and unavoidable impurities, or (ii) an annealed and pickled coldrolled steel sheet; preplating the steel sheet with between about 0.2g/m² and about 2.0 g/m² of Ni without rinsing or drying the steel sheetafter the pickling; preparing the steel sheet by heating the steel sheetin at least one of a nonoxidizing atmosphere or a reducing atmosphere toa sheet temperature of 430° C. to 500° C. at a rate of at least about30° C./sec; hot-dip plating the steel sheet in a galvanizing bathcomprising between about 0.05% and about 0.2% of Al; wiping the steelsheet; immediately heating the steel sheet to a temperature betweenabout 470° C. and about 550° C. at a rate of at least about 30° C./sec;and cooling the steel sheet to form the high-strength hot-dipgalvannealed steel sheet.
 23. The method of claim 20, wherein the steelsheet is cooled by at least one of (i) cooling the steel sheet withoutsoaking the steel sheet, or (ii) holding the steel sheet for soaking forless than about 10 seconds and then further cooling the steel sheet. 24.The method of claim 23, wherein the steel sheet comprises between about0.2% and about 3% of Si.